small hf antennas - north shore amateur radio · pdf file12/2/2006 nsarc hf operators 1 small...

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •

NSARC HF Operators 112/2/2006

Small HF Antennas

! The Small Space and Big Antenna Dilemma! Constraints

" Covenants" Restricted lot size" City Bylaws" Boards of Variance" Strata Rules" Neighbor complaints of unsightly “structures”" What else if that’s not enough?

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


The Challenge

! How to make HF antennas perform in small spaces

! Small antennas" Small means shorter antennas that fit available space

! How to make Stealth antennas" Ant’s that are visible but don’t look like antennas

! How to Hide antennas" Out of sight but somewhere in/on the housing structure

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Operating Issues

! Performance issues using short antennas" Lower gain – less “wire in the sky”" Narrower bandwidths – tuning required " Non-50 ohm feed point impedances – tuner needed

! Interference more likely" Proximity to audio, video, AM, FM, PC, Tel, etc equipment" QRP to 100 watts probable max

! Safety issue" You and the antenna may share the same space" RF biological exposure limits to be checked " Structural integrity of mounted antennas – make secure

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Building RF Transparency

! Conducting materials at ½ wavelength spacing

! Wooden frame structures " RF transparency - good" Internal conductors – “antennas”

! Power, telephone, cable, alarm etc wiring ! Copper plumbing

! Concrete structures" RF shielded at HF

! Rebar and metal framed windows – small aperture! Metal 2 x 4 framing inside building! Internal conductors

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Which Floor? Apt / Condo

! Top floor " access to roof top antennas " short feeder runs " best separation from tenants, none above

! Bottom " access to ground mounted antennas" grounding systems possible" feeder runs OK " tenant spacing, top & 2 sides

! Mid floors" interior or balcony mounted antennas" tenants all around

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Some Antenna Theory

! Basic antenna forms – only 2 !" Hertzian form" Marconi form

! Understanding Short antennas " Properties" Behavior " Performance

! What type might be best depends on circumstances

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Antenna Circuit

! Generator – the transmitter! Feedline – two conductors! Antenna – two wires ! Antenna as R = radiation resistance at resonance

! Complete the circuit - current must flow entirely around the loop

feedline antennatransmitter

current

current

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Hertzian Antenna

! No earth connection required for Antenna – good!! Antenna radiates independent of ground

! Rig grounded by green wire in power cord - SAFETY ! This ground is not part of the antenna system.

feedline

dipole

earth ground

safety ground

Balun

Transmitter

Dipole, half wave

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Marconi Antenna

! Antenna operates “against” ground.! Ground circuit is required – real earth or artificial! Ground is the other half of the antenna circuit! Ground consists of a conductive surface to

mirror the top half of the antenna

! Rig grounded by green wire in power cord - SAFETY! Safety ground could become part of antenna system! Not desirable

earth ground

feedline

vertical

safety ground

TransmitterVertical quarter wave

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Standard Antennato which most other antennas are compared

! Resonant Half Wave dipole

! At resonance, feed point ~ 50 ohms (radiation resistance)

" Good match to 50 ohm coax" Low VSWR" Maximum power transfer from rig to antenna

! Short antenna performance measured against this " gain, impedance, bandwidth,

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Short Antenna Properties

! Antenna no longer resonant at desired frequency

! Antenna gain is reduced due to shortness

! Feed point impedance changes" radiation resistance drops significantly " capacitive reactance appears at the feed point " feedline matching becomes poor and & high VSWR results

! Efficiency drops" ohmic losses become a significant part of the feed point Z

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Solutions

! Dipoles

! Loops

! Verticals

! Long (actually short) wires

! Other?

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Restore Resonance

! Short antenna “looks” capacitive

! Restore feed point impedance to look resistive

! Add an inductor somewhere “in” the antenna" nulls out the capacitance – creates resonant circuit" used with both dipoles & verticals

! Add a capacitor to the end of antenna" make antenna look longer (electrically) than it is" used most often with verticals

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Use an External Tuner

! Antenna is not brought back to resonance" no inductive or capacitive loading added

! Tuner matches complex antenna feed point impedance to 50 ohm output of transmitter

! Useful for multi-band operation

! Tuning limitations may be evident if tuner cannot match the antenna / feed line impedance.

! Rig tuners not well suited to off–resonant antennas

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Loading Coils

! Loading Coils are inserted in series with antenna " “makes up for shortness”

! Spi-Ro Manufacturing offers “Shortners”" http://www.spiromfg.com/

! Cancels the Capacitive component

! Resonates the antenna

! Coil placement " Dipoles – one in each leg" Verticals – one towards or at the bottom

http://www.spiromfg.com/

- • - • - - • - - • • • • • - • - - • • • - • • • • • - •

NSAR12/2/2006

Coil Loaded Dipole

! Balanced system! Single band! No ground issues! Reduce lengths

" 80m dipole from 132 ft to" 40m dipole from 66 ft to " most likely an outdoor ap

! Radio tuner ought to be O

B n

Loading Coils ( – “Shortner”
•
alu

2)

C HF Operators 16

69 ft38 ftplicationK



- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Wire Antennas

! Shortened, loaded balanced multi-band dipoles" No ground issues" Multi band " Outdoor

! Alpha Delta http://www.alphadeltacom.com/" DX-EE 40 ft / 40 thru 10" Radio tuner probably OK

! B & W http://www.bwantennas.com/" BWD series 20 ft / 20 thru 10m" Radio tuner OK

! Radio Works http://radioworks.com/" G5RV all band" External tuner needed

http://www.alphadeltacom.com/

http://www.bwantennas.com/

http://radioworks.com/

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Compact Dipoles

! Ventenna" 20 to 10m " 80 & 40m options " length unknown" http://www.ventenna.com/hfp-dipole.html

! Buddipole" 40 to 2m" coil loaded" collapsible" 16 feet extended" http://www.buddipole.com/

http://www.ventenna.com/hfp-dipole.html

http://www.buddipole.com/

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Compact Vertical

! Ventenna" 40 to 10m " 80m option" length 10’ 6” (3.2m)" http://www.ventenna.com/hfp-2.html

http://www.ventenna.com/hfp-2.html

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


MFJ Loop Antenna

! Small and very suitable for apartments! 36 inch diameter! No ground system required! MFJ-1786 20 thru 10m! MFJ-1788 40 thru 15 m! Good performance reviews on eHam! Low noise advantage! Self tuning – no external tuner needed! Inside or outside dwelling

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Wire Loop Antenna

! Home made - construct wire loop! Could reside inside dwelling ! Hang horizontal or vertical ! Requires external tuner & balun

" LDG Z-100 tuner + RBA balun" http://www.ldgelectronics.com

! No ground required! Random length loop – big as possible

earth ground

feedline

Loop

safety ground

TransmitterAuto

AntennaTuner

Balun

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Compact Yagi's

! Hybrid Quad" Model MQ-1" 20 thru 6m" 11 ft elements / <5 ft boom" http://www3.sympatico.ca/

! G4MH Mini Beam" 10 /15/ 20m 3 element" 2m boom / 5m elements

! ZX Mini-2000 Beam" 10/15/20m 3 element" 3m boom / 3.4m elements

! Both at http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=4044

http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=4044

http://www3.sympatico.ca/tgmc/

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Vertical Antennas

! Verticals are unbalanced antennas

! Require a ground plane or counterpoise

! Copper plumbing and Safety ground wiring NOT a good choice for RF ground / counterpoise.

! Mounting possible off balconies, rooftops or at ground level

! Inside a dwelling, maybe not so practical

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Radial SystemMultiwire

! A system of wires at base of vertical" minimum 2 per band if using multi band vertical" single band, try for 8 as long as possible, up to ¼ wave

! Lay radials out symmetrically as possible

! Bend ends to fit, no bends at base

! Lay radials on surfaces" roof, hold in place with bricks" lawns - trench and bury (staples avail. from DX Engineering)

Vertical

Radials

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


! A conductor(s) used as a substitute for earth or ground in an antenna system.

! Usually just one or two wires! Counterpoise will have RF on it and will radiate! Undefined operation if using building copper pipe

or safety ground wiring as counterpoise.! MFJ-931 Artificial Ground – loads a short

counterpoise

CounterpoiseSingle Wire

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Coil Loaded Vertical

! Coil at base = feed point

! Intended for mobile applications

! Uses car body as counterpoise

! Use as base with a radial orcounterpoise system

~ 5 feet highChange bands by Moving tap on coil

http://www.mfjenterprises.com/


- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Capacity “Hats”

! Capacity “Hat” placed at end (top) of antenna

! Resonates the antenna

! Removes the Capacitive component

! Placement most effective at end of antenna

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Capacity “Hats”

MFJ-1796

MFJ-1792

Capacity Hat

40 thru 2m No RadialsFeed line balun

12 feet high24” footprint

80/40mNeeds, guys & radials

33 feet high



- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


! Coax feedline to vertical – use a current choke / balun! Keep RF from flowing on coax & entering shack! Isolates rig / ant from safety ground! Coax coil choke

" CQ magazine Oct 2006 pg 44

! Snap On chokes" RF Parts or DX Engineering" http://www.dxengineering.com/" http://www.rfparts.com/choke.html

! Ferrite Beads" Palomar Engineering model BA-8" http://www.palomar-engineers.com/

Current Baluns

http://www.dxengineering.com/

http://www.rfparts.com/choke.html

http://www.palomar-engineers.com/

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Some Vertical Antennas

! Trap " Good for ground mount or flat roof" to 30 ft high" Requires ground system" Multi-band 80 thru 10m" MFJ http://www.mfjenterprises.com/" Hygain http://www.wb0w.com/hygain/hygain.htm

! Screwdriver" Motorized, tuneable" Multiband, fully resonant 80 – 10m " Extends to ~ 9 ft, some shorter" Requires ground system" High Sierra http://www.cq73.com/" Tarheel http://www.tarheelantennas.com/home


http://www.wb0w.com/hygain/hygain.htm

http://www.cq73.com/

http://www.tarheelantennas.com/home/

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


More Vertical Antennas

! Mobile Whip" Require ground system" Ham Sticks, monoband, ~ 6 ft

! http://www.hamstick.com/" Outbacker multiband ~ 7.5 ft

! Use Outpost tripod for ground mounting! http://www.alphadeltacom.com/pg9.htm

"

! Balcony Verticals" Designed for balcony mount" Require ground system" ~ 6 ft" Multiband 40 – 10m" MFJ 1622 " B&W AP-10A http://www.bwantennas.com/

Radials / counterpoises generally required.

http://www.hamstick.com/

http://www.alphadeltacom.com/pg9.htm

http://www.bwantennas.com/

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Balcony Mounted

! Short verticals mounted on railings" Metal railings as counterpoise" Wooden railings, run counterpoise

wires on wood or on floor; cover with mat

! Longer verticals" Painter pole, retractable, telescoping “mast”" Mobile whips " June 2006 TCA

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


More Balcony Mounts

! http://www.eham.net/forums/AntennaRestrictions! Pigeon “preventors”! Ideas, reviews, comments ….

http://www.eham.net/forums/AntennaRestrictions/

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Long Wire Antennas

! Random lengths of wire – long as possible " easy to build – string outdoors, #22 insulated black " need to support two ends

! Typically non resonant

! Usually end fed – high Z point

! Must have a tuner (other than rig)

! Tuner must have a “ground” or counterpoise connection

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Stealth

! ARRL Book! Flagpole Verticals – ground mounted! Wires lying on roof tops

" Black insulation, small dia, #22! Wires on Gable ends

" No good under AL eaves with AL gutters! Wires on Fences - Loops! Attics for yagi’s! VHF/UHF on short mast looks like TV antennas! Vent pipe VHF/UHF verticals, roof mounted

" Ventnna

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Subsurface DipoleReally ??

! If on ground floor and able to trench the yard" Buried ~ 8 inches

! Reported 16dB less gain" ~ 3 S points less than a comparable, low dipole

! Rather “experimental”

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Safety

! Exposure to RF fields " Biological heating" Safety Code 6 – Canadian Standard

! http://strategis.ic.gc.ca/epic/internet/insmt-gst.nsf/en/sf01635e.html" Exposure Factor - closeness to antenna " Exposure Factor - transmitter power levels

! Antenna Voltages " RF burns from ends of antennas " “Hot” grounds at unknown locations if safety ground or

plumbing used as counterpoise

http://strategis.ic.gc.ca/epic/internet/insmt-gst.nsf/en/sf01635e.html

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Exposure Calculation

! Approximates Safety Code 6 – uncontrolled environment! Calculate safe field strength

http://n5xu.ae.utexas.edu/cgi-bin/rfsafety.cgi

Calculation Results Average Power at the Antenna 20.000 watts

Antenna Gain in dBi 0.00 dBi Distance to the Area of Interest 5.00 feet

Frequency of Operation 20.000 MHz Are Ground Reflections Calculated? No

Estimated RF Power Density 0.0686 mw/cm2

ControlledEnvironment

UncontrolledEnvironment

Maximum Permissible Exposure (MPE) 2.25 mw/cm2 0.46 mw/cm2

Distance to Compliance From Center of Antenna 0.92 feet 2.00 feet

Does the Area of Interest Appear to be in Compliance? yes yes

Calculate Radio Frequency Power Density What is the average power at the antenna: In watts

20

What is the antenna gain in dBi: Enter 2.2 for dipoles; add 2.2 for antennas rated in dBd

0

What is the distance to the area of interest: From the center of the antenna, in feet

5

What is the frequency of operation: In MHz

20

Do you wish to include effects of ground reflections? Yes No

Calculate RF Power Density Reset Values

http://n5xu.ae.utexas.edu/cgi-bin/rfsafety.cgi

- • - • - - • - - • • • • • • - • - - • • • - • • • • • - •


Summary

! Consider balanced antenna systems first

! Verticals work will work but require radials or counterpoise

! Long wires will work but require counterpoise

! Try and get the antenna outside somewhere

! Do not create a ”special” station RF ground – the radial or counterpoise is your RF ground

! Keep antenna away from metallic objects" Aluminum window frames" Service entrance

! If moving, choose antenna friendly site

small hf antennas - north shore amateur radio · pdf file12/2/2006 nsarc hf operators 1 small...

Documents